The LCD light source module is one of the critical components in LCD technology responsible for providing uniform and sufficient light on LCD panel. Since the light source module consumes more than 50% of the power in a LCD, it is a relative important subject of LCD technology to provide uniform light of desired brightness under limited power available.
There are two types, i.e., back lighting and front lighting, of light source module; the back lighting type can be classified into edge lighting form and bottom lighting form in accordance with different incident position while the front type can only be an edge lighting form. Currently, two to eight edge lighting lamps are used together with a light guiding plate and an optical film to provide light source of high evenness and efficiency for LCD products of less than 20 inches in size. Bottom lighting backlight module has become the main stream in the light source of large LCD monitors/televisions due to more rigorous characteristics on brightness and view angle are required on such products. However, the bottom lighting backlight module needs more lamps and greatly increases the cost in comparison to an edge lighting module. On the other hand, adding the number of lamps may result in problems on heat dissipation and power consumption, thereby making improvement on the structure design has become a key factor for the manufacturer to success in the development of new product.
FIG. 1 is a schematic view showing a bottom lighting light source module of prior art. As shown in the figure, a twelve-lamp backlight module used in a twenty-three inches panel has a total thickness of 25 to 30 mm and a 4.8 mm space between adjacent lamps. In general, such light source module can provide brightness evenness from 65 to 75%, while a high standard module of such kind can provide a brightness evenness of up to 85%.
A typical bottom lighting backlight module as shown in FIG. 1 comprises a light reflecting plate 1 one side of the lamp array and a light diffusion sheet 2 on the opposite side of the light reflecting plate, wherein prisms are adhered to the upper or lower surface of the diffusion sheet. In some case, modifications of patented shapes such as triangular or circular pillars are made on the light reflecting plate to redirect the light from a bright area or position right beneath the lamp to a dark area or a position located between bright areas. Most of the manufacturers simply use a flat light reflecting plate (see U.S. Pat. Nos. 5,253,151 and 5,720,545); reduce the brightness of the diffusion sheet on area right above each lamp by applying certain material to these areas and increase light emitted from dark area by mixing highly reflective material such as titanium dioxide in said diffusion sheet; or average the brightness evenness on the diffusion sheet by forming microstructures on the diffusion sheet (see U.S. Pat. Nos. 5,986,728 and 6,421,103). Furthermore, it is difficult to reduce the thickness of entire backlight module 4 to less than 1 cm while maintaining high evenness in its brightness. It is also difficult to achieve a brightness with evenness higher than 80% by means of a diffusion plate thicker than 2 cm.